Information storage devices are used to retrieve and/or store data in computers and other consumer electronics devices. A magnetic hard disk drive is an example of an information storage device that includes one or more heads that can both read and write, but other information storage devices also include heads—sometimes including heads that cannot write. For convenience, all such heads may be referred to as read heads herein.
Referring now to FIG. 1, a contemporary hard disk drive 100 includes a disk drive base 102, at least one disk 104 (such as a magnetic disk, magneto-optical disk, or optical disk), a spindle motor 106 attached to the base 102 for rotating the disk 104, and a head stack assembly (HSA) 110. The spindle motor 106 typically includes a rotating hub on which disks are mounted and clamped, a magnet attached to the hub, and a stator. Various coils of the stator are selectively energized to form an electromagnetic field that pulls/pushes on the magnet, thereby rotating the hub. Rotation of the spindle motor hub results in rotation of the mounted disks. The HSA 110 typically includes at least one actuator arm 114, and at least one head gimbal assembly (HGA) 124 that includes a read head.
During operation of the disk drive, the HSA 110 rotates to position the read head along an arc adjacent desired information tracks on the disk 104. The HSA 110 includes a pivot bearing cartridge 118 to facilitate such rotational positioning. The HSA 110 typically includes a voice coil that interacts with one or more fixed magnets on a magnetic yoke 112, to rotate the HSA 110. For example, when the HSA 110 is rotated such that the HGA 124 leaves a ramp 120, the read head is loaded onto a surface of the disk 104. Other contemporary disk drive components shown in FIG. 1 include a flex cable bracket 116 and a recirculation air filter 108.
In magnetic hard disk drives, each read head typically comprises a body called a “slider” that carries a magnetic transducer on its trailing end. The magnetic transducer typically comprises a writer and a read element. The magnetic transducer's writer may be of a longitudinal or perpendicular design, and the read element of the magnetic transducer may be inductive or magnetoresistive (e.g. so-called “giant” magneto-resistive read element, tunneling magneto-resistive read element, etc). In a magnetic hard disk drive, the transducer is typically supported in very close proximity to the magnetic disk by a hydrodynamic air bearing. As the motor rotates the magnetic disk, the hydrodynamic air bearing is formed between an air bearing surface of the slider of the read head, and a surface of the magnetic disk. The thickness of the air bearing at the location of the transducer is commonly referred to as “flying height.”
Magnetic hard disk drives are not the only type of information storage devices that have utilized air bearing sliders. For example, air bearing sliders have also been used in optical information storage devices to position a mirror and an objective lens for focusing laser light on the surface of disk media that is not necessarily magnetic.
The flying height is a key parameter that affects the performance of an information storage device. If the flying height is too high, the ability of the transducer to write and/or read information to/from the disk surface may be substantially degraded. Therefore, reductions in flying height can facilitate desirable increases in the areal density of data stored on a disk surface. However, it is not beneficial to eliminate the air bearing between the slider and the disk surface entirely, because the air bearing serves to reduce friction and wear (between the slider and the disk surface) to an acceptable level. Excessive reduction in the nominal flying height may degrade the tribological performance of the disk drive to the point where the lifetime and reliability of the disk drive become unacceptable.
Another factor that can adversely affect the tribological performance of the read head, and therefore also adversely affect the disk drive's lifetime and reliability, is the extent to which particulate debris can enter the air bearing during operation. Because the thickness of the air bearing is just a few tens of nanometers or less (typically minimum at the trailing edge of the slider because of the slider's positive pitch angle), even small debris particles can be large enough to interfere with the desired spacing between the air bearing surface and the disk surface. Such particulate debris that enter into the air bearing can undesirably cause abrupt thermal disturbances to the read element and/or temporarily change the flying characteristics of the slider, potentially causing immediate reading or writing errors. Such debris that enter into the air bearing can also drag along the disk surface and possibly damage the disk surface, potentially destroying data and/or leading to future tribological failure (e.g. head crash).
Air bearing features that discourage the entry of particulate debris have been proposed before. For example, U.S. Pat. No. 5,490,025 to Dorius et al. discloses a debris deflecting feature in an air bearing design. However, past air bearing design features that discourage the entry of particulate debris have been detrimental to the flying characteristics of the slider, for example reducing super-ambient pressure in key regions of the air bearing and thereby unacceptably reducing the load carrying capacity of the air bearing. Certain such design features can also adversely affect the ability of the air bearing to maintain an acceptable roll angle in the face of expected changes to the skew angle of the slider (relative to the direction of disk surface motion). Such skew angle changes are expected as the actuator positions the read head to different disk radii. The shortcomings of contemporary air bearing design features to discourage entry of particles may be exacerbated in sliders having a smaller air bearing area, such as newer smaller-form factor sliders (e.g. the so-called “femto” form factor).
Accordingly, what is needed in the art is an air bearing design that can discourage the entry of particulate debris while maintaining acceptable air bearing performance characteristics even in small form factor sliders.